Work is proceeding on three fronts. These are studies of inorganic materials appropriate for use as pit and fissure sealants, studies of the effect of increased temperature on the fluoride uptake of tooth enamel, and studies to define the pertinent damage thresholds for the use of lasers on human teeth. All work is oriented toward answering questions regarding the evaluation of the use of a laser for preventive dentistry techniques. Materials work is directed toward the development of an enamel-like substance that can be permanently appplied to the pit and fissure area of the molars. Sintering apatitie materials has been explored, and other techniques requiring lower temperatures are being examined. An analytical model for fluoride uptake has been formulated assuming diffusion with slow chemical reaction. Work is now proceding to evaluate this theory. This includes the measurement of fluoride profiles that result from a wide variety of treatment conditions. Preliminary data indicate that laser heating greatly enhances the uptake. Microscopic damage thresholds resulting from laser energy absorption are being examined. Earlier tests have shown that damage to vital tissues can be easily circumvented, but potentially with resulting damage to the enamel surface due to thermal stresses. This is being examined.